The present invention relates generally to an image processing apparatus, and more particularly to an apparatus for forming a digital image by carrying out an image processing appropriate for an input image supplied by a scanner, so that the digital image is output by a printer for recording.
In an image processing apparatus, it is desirable to take some measures which allow a high quality digital image to be formed from an input image supplied by a scanner no matter what the characteristics of the input image are. For example, Japanese Laid-Open Patent Application No.2-84879 discloses an image processing apparatus in which an image processing suitable for an input image is selected to output a high quality image. In this apparatus, an input unit for inputting an input image obtained by scanning an original document, an output unit for outputting an image after an image processing is carried out, and a detection unit for detecting characteristics of the input image supplied by the input unit are provided. Based on the characteristics of the input image detected by the detection unit, the kind of the scanned document is discriminated and an image processing suitable for the characteristics of the input image is selected and carried out so that the output unit outputs a high quality image. For example, if it is detected that the document has a character image, an image processing suitable for the character image is selected. If it is detected that the document has a continuous tone image (or a photograph image), an image processing appropriate for the photograph image is selected. And if it is detected that the document has a screened dot image, an image processing suitable for the screened dot image is selected. However, it is required that the above mentioned apparatus define, in advance, the one-to-one correspondence between each of the input image characteristics and each of the image processing procedures suitable therefor. The same requirement is also applicable to filtering processes which are carried out as a kind of image processing. It is also required that the above mentioned apparatus define, in advance, the one-to-one correspondence between each of the input image characteristics and each of the filtering processes.
In order define the one-to-one correspondence mentioned above, all possible combinations of detected image characteristics of an input image must be predetermined. Recently, in an image processing apparatus, it has become desirable and necessary to predict a great number of combinations of detected image characteristics. As the number of the combinations is increasing, realization of such an image processing apparatus in which a desired image processing can be selected for any kind of image characteristics becomes more and more difficult. In the case of the filtering processes, for example, the use of edge intensifying (or edge emphasizing) processes with several low and high levels and smoothing processes with several low and high levels in an image processing apparatus is desirable to reproduce a high quality image. However, it is difficult to predetermine all possible combinations of detected image characteristics to predefine the one-to-one correspondence between each of the image characteristics and each of the filtering processes suitable therefor. Even if it were possible to take the above mentioned measures, it would be difficult to select a suitable filtering process from several processes. In addition, it is necessary to use several filters provided in parallel in an image processing apparatus for switching a filtering process in response to the detected image characteristics so that a suitable filtering process is carried out, and as such an apparatus is bulky, it is not suitable for practical use.